1. Field of the Invention
The present invention relates to a bootstrap capacitor detecting circuit and a bootstrap DC-DC converter, and more particularly, to a bootstrap capacitor detecting circuit and the bootstrap DC-DC converter thereof capable of discharging a bootstrap voltage node and then determining whether a bootstrap capacitor is connected normally according to whether a bootstrap voltage is significantly reduced.
2. Description of the Prior Art
Power supply devices play important roles in the modern information technology. Among all the power supply devices, DC-DC converters have been widely used, and are mainly utilized for providing a stable output voltage for electronic elements.
In short, please refer to FIG. 1, which is a schematic diagram of a conventional bootstrap DC-DC converter 10. As shown in FIG. 1, when a clock signal VCLF is with logic high to trigger a set terminal S of an SR flip-flop 100, the SR flip-flop 100 continues to output a control signal CON in logic high to a pre-driving unit 102. Therefore, the pre-driving unit 102 controls an upper gate driving unit 104 and a lower gate driving unit 106 to output an upper gate control signal UG and a lower gate control signal LG accordingly, such that the upper gate switch 108 is turned on and the lower gate switch 110 is turned off, to output an inductance current IL and a corresponding output voltage VOUT for a loading RLOAD. Then, when a feedback voltage VF (a divided voltage from the output voltage VOUT) exceeds a reference voltage VREF, an error amplifier 112 outputs an error signal EAO to indicate a pulse width modulation (PWM) control loop 114 to reset a reset terminal R of the SR flip-flop 100, such that the SR flip-flog 100 outputs the control signal CON in logic low. Therefore, the pre-driving unit 102 turns off the upper gate switch 108 and turns on the lower gate switch 110 accordingly until the clock signal VCLK switches to another logic high to trigger the set terminal S of the SR flip-flop 100. Then, the above operations are repeated.
When the lower gate control signal LG is with logic high such that the lower gate switch 110 is turned on, a switch 116 (including a body diode 118) conducts connection between a system voltage PVCC and a bootstrap capacitor CBOOT to charge the bootstrap capacitor CBOOT. Therefore, when the control signal CON is with logic high to turn on the upper gate switch 108, a driving voltage of the upper gate driving unit 104 is high enough to turn on the upper gate switch 108, wherein a bootstrap voltage VBOOT of a bootstrap voltage node BOOT, which is coupled to an input terminal of a driving voltage of the upper gate driving unit 104, is an input voltage VIN plus a voltage across the bootstrap capacitor CBOOT (i.e., the system voltage PVCC), and the drain-source voltage of the upper gate switch 108 is the bootstrap voltage VBOOT. The operation of the bootstrap DC-DC converter 10 is well-known for those skilled in the art, and hence the details are omitted herein.
For this structure, if the bootstrap capacitor CBOOT is not connected normally during the manufacturing process (such as false welding or lose efficacy, that is, the bootstrap capacitor CBOOT is ineffective, causing the system voltage PVCC to charge parasitic capacitor), the upper gate driving unit 104 can not be effectively driven by the bootstrap voltage VBOOT to completely turn on the upper gate switch 108. Therefore, when the upper gate switch 108 outputs the inductance current IL, the upper gate switch 108 could be burned out due to large power. Thus, there is a need for improvement of the prior art.